Automatic pilot systems for marine vessels are generally characterized by following a compass heading, and if the vessel should deviate from a given course, an error signal is generated causing a control circuit to drive a rudder or other steering control so as to correct for the deviation. Any number of autopilot systems have been developed in the past to accomplish this desired end. For the most part, these systems will sense the magnitude of error or change in course with respect to a reference setting, such as for instance, by averaging compass heading indications or by employing a digital disk. Typical of such approaches are those disclosed in U.S. Pat. Nos. 3,833,901 and 3,975,621 to J. T. Fowler, and 4,040,374 to L. M. Greene.
In my copending application for patent, Ser. No. 405,986, filed Aug. 6, 1982 and entitled "Autopilot System", another type of autopilot system is disclosed for steering a marine vessel and maintaining it on a predetermined course through the combination and arrangement of an incremental encoder together with a heading reference circuit. There, an encoder includes circuitry which will generate a directional signal and count pulse for each increment of movement from the vessel away from a preset heading, and the heading reference circuit has adjustable reference setting means which will set a counter at a reference position corresponding to the preset heading, the counter being responsive to the pulses received from the encoder to count either in a positive or negative direction depending upon whether the pulses received are either positive or negative with respect to the reference position. A correction signal is then generated to drive an analog device for a steering control mechanism, such as, a rudder in order to return the vessel to its preset heading or course.
In the instant invention, it is proposed to provide an error sensing system with an absolute zero or null position that will not drift with time or temperature but at the same time is greatly simplified while avoiding errors that could otherwise result from changes due to component aging, voltage changes, temperature variations and the like, and further obviates the use of relatively complex or sophisticated electronic circuitry. Moreover, the system as devised is extremely versatile and readily conformable for use with various types of marine craft including sailboats.